In recent years, there has been continuing interest in liquefying natural gas and other light hydrocarbon gases at remote sites where there is little or no nearby market for the natural gas. Natural gas located at such remote sites is of market value only if it can be pipelined or otherwise transported to a marketplace. In many instances, it is not feasible to construct pipelines to transport such natural gas. Therefore, in many instances it has been found desirable to liquefy the natural gas on site so that it can be transported by tanker to markets.
A variety of processes for liquefying natural gas are known. In most of these processes, the natural gas is treated to remove acid gases, water and hydrocarbons heavier than about C3 as necessary prior to liquefaction. Known refrigeration processes comprise processes that may use multiple pure component refrigerants, multi-component refrigerants or combinations thereof. Refrigeration processes using one or more refrigerant sections and the like may be used. A variety of such processes are known and could be used with the present invention. All such processes generally require that a compressed refrigerant be made available at a pressure such that upon cooling it can be liquefied and thereafter vaporized to produce the refrigeration required to liquefy the natural gas.
Most such processes are quite energy intensive and require substantial energy input to compress the refrigerant for repeated cycling through a refrigeration zone to produce the refrigeration necessary to at least partially liquefy the natural gas and the like. Further, substantial energy may be required in many instances to recompress the natural gas after treatment to remove acid gases and water from the natural gas or to remove heavier hydrocarbons from the natural gas. All these processes typically require large quantities of electrical power and mechanical energy with the resultant emission of large quantities of carbon dioxide (CO2) into the atmosphere.
Recently it has been considered that release of CO2 into the atmosphere is detrimental to the atmosphere. Accordingly, it has been deemed desirable that the amount of CO2 emitted in such processes should be reduced. Typically such processes have been operated in areas where there was an abundance of cheap fuel. Therefore, little concern has been directed to limiting the emission of CO2 into the atmosphere since it was more convenient and economical to simply discharge combustion exhaust streams into the atmosphere than to limit the amount of fuel consumed since such fuel is readily available at little or no cost at the liquefaction site. As well known to those skilled in the art, hydrocarbon fuels, especially light hydrocarbon gases, have been used widely for generation of electrical power and for production of mechanical energy via light hydrocarbon gas fired turbines and the like.
Recently, it has become apparent that it would be desirable to provide a system and a process for providing compressed refrigerant and electrical power for a light hydrocarbon gas liquefaction process wherein reduced emissions of CO2 were produced and wherein the mechanical energy and electrical power for the process could be produced on site.